A human ovary contains many thousands of germ cells distributed throughout its stroma, each of which is surrounded by a small number of specialist cells to create a primordial follicle. These follicle complexesbegin to develop one by one throughout reproductive life in response to gonadotrophin hormones secreted by the pituitary glandbut they only become visible to ultrasound in their later stages of development when they develop a fluid-filled antrum. These fluid filled follicles give the ovary its characteristics appearance during the reproductive years.

In the present day practice, serial ultrasound monitoring of the graafian follicle is used to detect ovulation in patient undergoing Rx for infertility.